Concealers are excellent to camouflage blemishes, sunspots and to eliminate redness and dark eye circles.
The right concealer shade depends on your skin tone and the areas of you face to want to conceal. For most complexions yellow base tones looks the most natural. For dark or black toned skin try using an orange based concealer and avoid and concealers with a hint of white in them (as they tend to highlight your blemishes and turn into a dirty shade of gray. To cover dark eye circles it is recommended to use a tone slightly lighter than your skin tone or a yellow/peach toned concealer to offset the dark pigment underneath your eyes.
For blemishes and discolorations look for a colour that best matches your skin tone exactly. The closer the concealer matches your skin the less concealer you will need to apply and giving you a more nature finish.
To conceal redness try using a green or yellow concealer to offset the red. To help combat yellow tones you can use a purple coloured concealer to make your skin look brighter and rosier.
When buying concealer in store try the concealer specifically wear you plan to wear it and always look at it in natural daylight.
It is recommended to use a concealer wheel as they provide all the necessary colours and tones to help conceal your imperfections, plus you can mix and match for your skin tone.